Multicolor thermosensitive paper

ABSTRACT

A multicolor thermally sensitive paper having a supporting substrate with a first coat of material normally of a first color reacting in response to a given quantity of heat to turn into a contrasting color with a second coat overlaying the first coat in the form of an opaque blush coat thermally adapted to be transparentized in response to a quantity of heat lower than the given quantity.

United States Patent Truitt et a1. 45 D 2, 1975 1 1 MULTICOLOR THERMOSENSITIVE PAPER 3.377.165 4/1968 Workman 117/367 x n H 3.442.682 5/1969 Fukawa 117/368 [75] lnvenmrs- James Dana, RObertC- 3.481.760 12/1969 Clark ctal 117 362 both of 3.647.503 3/1972 Mizutzmi ct 111 117 364 [73] Assignee: Texas Instruments Incorporated, 3,792,481 2/1974 Nagashima et a1. 346/1 Dallas. Tex. Primary Examiner-Thomas J. Herbert, Jr. [22] F'led: July 1973 Attorney, Agent, or Firm-Harold Levine; Rene E. [21] APPL 333,922 Grossman; Thomas G. Devine 152] U.S. C1. 428/411; 427/145; 427/148; [57] ABSTRACT 42 535; 428/537 A multicolor thermally sensitive paper having a sup- 151 int. c1. B41M 5/18 Porting substrate with a first Coat of material normally [58] Field of Search 1 17/368, 36.2, 36.4, 36.7; of a first Color reacting in response to a given q y 96/29 of heat to turn into a contrasting color with a second coat overlaying the first coat in the form of an opaque [5 References Cited blush coat therm'ally adapted to be transparentized in UNITED STATES PATENTS response to a quantity of heat lower than the given uantit 2,663,654 12/1953 Miller ct a1. 117/368 q y 3.094.619 6/1963 Grant 117/368 X 10 Claims, 2 Drawing Figures US. Patent Dec. 2, 1975 3,924,049

commonly on the market, to further break it down to micron size particles, for example, on the order of 1 micron. Solution A, as prepared with the finely divided iron stearate, is relatively stable, although it may need shaking after standing a substantial period in order to thoroughly redispense the ferric stearate.

In the preparations of Solution A and Solution B, referred to above, the solutions are prepared separately. Prior to their utilization, they are mixed in equal weights and applied to the white base stock 10, as illustrated in H0. 1. On the order of about 7 to 10 pounds of the mixture of A and B is generally required to cover 1,000 square foot, although varying thickness of layers will be desired in some instances. A typical coating thickness, when on a wet basis, is about 3 to 6 mils, but when dried the thickness is typically on the order of to 10 microns.

The application to the paper of the mixture of Solution A and Solution B is accomplished by well known art means, for example, the utilization of a Mayer bar machine or the utilization of reverse roll coating technique, well known in the art. If only a small specimen is desired, application may even be accomplished by a small hand-manipulated roller. In general, the Mayer bar is themost practical for hand application.

After the application of the mixture of Solution A and Solution B, and drying, the step of applying layer 11 of thermally sensitive red coating is completed.

The next step is to apply a layer 12 of a blush coating. The preparation of the blush coating material in this example. involves mixing 170 grams of a 4 percent methyl cellulose solution (in water) with grams of a white crystalline wax of low solubility in the solvent system (in this case, water). Many waxes are commercially available on the market that will fulfill this function and selection may readily be made for such purpose; however, in this example, the particular wax utilized is that commonly available commercial material known as Hoechst V. It is necessary to thoroughly ball mill the mixture in order to divide the wax into quite small particles, on the order of 1 micron size, in the solution. Different periods of time may be involved, depending on the particular ball milling equipment used and the various operating conditions, but exemplary of a ball milling time is 19 hours. There is the tendency toward formation of foam during ball milling, and a small quantity, for example 5 drops, of any typical anti-foam agent (such as that commercially available as Pegosperse) may be added to inhibit this foaming tendency. While this step is not critical, it is helpful in many instances. In performing this particular example, 16 hours of ball milling was accomplished, then the five drops of anti-foaming agent were added, and then three more hours of ball milling were performed. The end product obtained is applied to overlie the layer 11 (FIG. 1) to form the top blush" coating layer 12. The same techniques for coating referred to in conjunction with applying the layer 11 may be utilized. The coating applied in this particular example was applied by a Mayer bar and was, when dry, of approximately 10 microns thickness. Layer thickness may vary considera bly, depending on the nature of the underlying layer 11, its color intensity, the particular wax utilized, and other related factors. The object is to apply a coating of suit able thickness to mask the underlying layer 11, yet on the other hand that is not so thick that the paper become unduly bulky or such that the heat applied to the selected areas does not cause the desired blush effect underlying the points of heat application.

The end product, comprising the base paper 10 with the layer 11, made up of Solution A and B, as described above, and layer 12, made up of the particular wax coating as described above, is tested and found to be satisfactory for two color printing. Thus, on low range heat application, the upper layer 12 transparentizes in the specific regions where a proper level of heat is applied to form a transparent area which permits the viewer of the paper to see the underlying layer 11. If the heat level is low, the viewer sees the red color of layer 11. If the heat level is higher, then the material in the lower layer 11 reacts to cause a color change. It should be noted that the active ingredients in this reac' tion are ferric stearate and the 2,4,5 trihydroxybutyrophenone. Under the conditions where the red dye is omitted, the color formed by the reaction is green; however, the color change accomplished by the reaction, in the layer 11 permeated by the red dye, causes the visible color to be black.

It will therefore be noted that Example 1 effectively provides printing in two colors, red and black, selectively obtained in predetermined regions of heat application, the color visible to the observer being dependent upon the degree of heat applied to the preselected regions.

EXAMPLE 2 Example 2 utilizes a somewhat different material for the coating of the underlying layer 11. It is derived, in essence, from US. Pat. No. 2,663,654, to C. S. Miller et al. As stated in that patent under Example 1 cited therein:

Reactant A To an aqueous solution of three moles of the sodium soap of commercial triple-pressed stearic acid of melting-point approximately 53 C., and which supposedly contains a minor amount of other higher fatty acids, etc., add an aqueous solution of 1 mol of ferric sulfate. Filter the precipitated ferric stearate, wash separately with water and alcohol, and dry at room temperature. The solid product softens or melts within the range of -95 C. Disperse 500 grams of the powder in 2 liters of denatured ethyl alcohol, e.g.-, Pensolve," by grinding with flint pebbles in a ball mill.

Reactant B Dissolve 1500 grams of hexamethylenetetramine in 12 liters of denatured alcohol (Pensolve) at 65 C; with constant stirring; add this solution to a solution of 2000 grams of pyrogallic acid in 4 liters of the alcohol, also at 65 C. A crystalline precipitate forms. Cool to room temperature, with constant stirring to avoid lumping. Recover and dry the precipitate, which should be in the form of a fine powder. Disperse 500 grams of this powder in one and one-half liters of denatured alcohol by ball milling as for Reactant A.

Reactant C Dissolve 10 grams of oxalic acid in milliliters of ethyl ,alcohol.

MULTICOLOR THERMOSENSITIVE PAPER This invention relates to a multicolor thermally sensitive paper and to a process or producing the same wherein color selection is dependent upon the quantity of heat transferred to the paper in a print operation.

Development of heat sensitive papers has led to the widespread use thereof in oscillographic recording devices and various types of printers.

Sheet materials have been specifically designed as copy paper. Such paper, when placed in contact with the surface of an original and the original is strongly and briefly irradiated, the heat is selectively absorbed by areas of the original to form a graphic message on the copy sheet. The absorbed radiation is converted to heat energy in a pattern corresponding to the graphic subject matter and the heat flows into the sensitive layer to convert the corresponding areas thereof to a visibly distinct form. In other systems, print heads having dot matrices thereon which are selectively energized to heat the same can be employed for direct printing rather than copying.

Heat sensitive sheets have previously been known in which opaque blushed lacquer coating is transparentized by heat or other agency to produce visible changes. The effect has been accomplished by compaction of soft coherent blush coating or by the fusion of a blushed lacquer or by the fusion of waxy or other fusible particles within blushed coatings of nonfusing binders. In general, the preparation of blushed lacquer coatings is well known and as usually practiced involves applying a thin coating of film-forming organic polymer from a solution of a mixture of a volatile liquid solvent and a less readily volatile liquid in which is a nonsolvent for the polymer followed by evaporation to make the polymer insoluble.

There has not heretofore been available a multicolor thermally sensitive paper to permit color selection dependent upon the quantity of heat transferred to the paper. The present invention provides such a paper capable of multicolor presentation.

In accordance with one aspect of the invention, a heat sensitive sheet material is provided in which a supporting substrate has a pair of heat actuable coats thereon. One coat is on top of the other. The top coat is actuable by application of heat of quantity less than the quantity of heat required for actuating the lower coating to provide for two color presentation of information.

For a more complete understanding of the present invention and for further objects and advantages thereof, reference may now be had to the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a sectional view of a two layer embodiment of the invention; and

FIG. 2 is a sectional view of a three layer embodiment of the invention.

Referring now to FIG. 1, it illustrates a cross section of paper produced in accordance with the present invention wherein the base paper layer is provided with a thermally sensitive red coating 11 on top of which is a second coating of low temperature blush material 12. The forming of the paper involves application of the thermally sensitive coating 11 to a base stock, with the thermally sensitive coating either permeated with or further coated with a red ink or dye. One

method of making base layer 11 is to deposit on base layer 10 a mixture of an iron soap, e.g. ferric stearate, and a diphenolic (e.g. 2, 4, 5, trihydroxybutyrophenone) together with a suitable binder and a red dye dispersed throughout. The iron soap and the phenolic compound react, in the absence of dye, to form a normally dark green compound when a given quantity of heat is applied thereto. Because of the presence of the red dye, the color obtained as a result of the heat initi ated reaction is black rather than green. Below the threshold heat level of the reaction, the red dye in the material causes it to appear as a red coating since the heat initiated reaction does not occur.

The low temperature blush coating 12 is an opaque white coat which is transparentized with the application of a quantity of heat lower than that necessary to cause reaction of the active components in the coating. Thus, upon application of a low quantity of heat to the blush coating 12, it will become transparent to expose the red dye layer therebelow. This would give the paper a red print corresponding with the outline of the heat applicator. Additional heat applied develops (through chemical reaction) the thermally sensitive coating 11 producing its green color to blend with the red dye and cause the ultimate appearance of a black image to the viewer.

The following examples are representative of FIG. 1.

EXAMPLE 1 Two solutions, for convenience hereinafter referred to as Solution A and Solution B, are prepared in accordance with the following recipes:

The particular dye of Solution B is commercially available from Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen am Rhein, Germany, under the trade name or mark Red-4R. It is an oil soluble dye. It is noted that substantially any dye producing a desirable red color may be utilized, although in this particular example it is desirable that the dye be oil soluble, as contrasted to water soluble, since the solvent system is acetone, an organic solvent. Note also that red pigment can be substituted for the dye and would be workable in this embodiment.

It should be noted that the iron stearate utilized in the mixing of Solution A should be of a fine particle size since it is not a soluble type material and requires a small physical configuration in order to form a relatively stable suspension. The iron stearate is suitably suspended by ball milling iron stearate powder, as is Binder Dissolve 150 grams of polyvinyl butyral in 1 liter of ethyl alcohol. The final composition, obtained on mixing the foregoing, has the following composition:

Rcactant A 500 ml. Reactant B I00 ml. Rcactant C (optional) 40 ml. Binder 300 ml.

In the foregoing described system, the ultimate composition in liquid form has added to it approximately one-fourth of 1 percent, by weight, due such as the dye utilized in Example 1 hereof. Any oil soluble dye may in general be utilized in this present example. The composition in liquid form, which is carefully mixed, is evenly spread over the paper base to form the thermally sensitive coating 11.

Thereafter, an overcoating layer, i.e blush coating layer 12, is applied using the same composition and same method of application as in Example 1 hereof.

The end product is a thermally sensitive paper which prints red or black, depending on the level of heat applied.

EXAMPLE 3 Example 2 is repeated, except as explained in the prior Miller et al. US. Pat. No. 2,663,654, the layer 11 is obtained by utilizing the technology of Example 2 of said patent, which involves ferric myristate, made with commercial mystric acid, in place of the ferric stearate referred to in the preceeding Example 2 hereinabove, and in using a reaction product of hexamethylenetetramine and gallic acid (a substituted trihydroxybenzene) in place of the pyrogallic acid product described in the preceeding Example 2 herein.

Other examples are contained in the referenced Miller et al. patent, and in general, provided that a dye of the desirable color be added, will product the desired reactive layer 11.

The blush layer is prepared in accordance with Example 1 herein to form the completed thermally sensitive paper.

EXAMPLE 4 This example involves the utilization in part of the certain technology described in US. Pat. No.

Formula for Suspension Liquid A:

Parts (by weight) Diphcnylthiocarbazidc L8 Sodium turtaratc 0.9 Polyvinyl butyral 8.9 Methyl alcohol 87.0

Formula for Suspension Liquid B:

Parts (by weight) Calcium ()lcatc Stearic acid Polyvinyl butyral Methyl alcohol 87.0

On mixing, a dye, for example, red dye in quantity weight of about /8 to A; weight percent is added to the combined mixtures of Suspension Liquid A and Suspension Liquid B. The resulting product is spread over the base layer 10, to produce a layer 11 in accordance with FIG. 1.

In general, the various descriptions and examples of US. Pat. No. 3,442,682 may be utilized in conjunction with the preparation of a suitable layer 11 in accordance with the present invention, and reference is therefore made to that patent for those desiring additional detail on options. Other systems, and refinements on those described, which may be utilized in conjunction with the preparation of a layer 11, are described in US, Pat. No. 3,481,760, Clark et al, and No. 3,094,619, Grant. Of course, it should be borne in mind that a dye must be utilized with the particular system selected.

EXAMPLE 5 Example 1 herein is repeated except the blush coating 12 is prepared in accordance with the following recipe (by weight):

Ethylccllulosc (ethoccl N-ZOO) 50 parts p-DiaZO-Z.5dibutoXybcnzoylaniline zinc chloride double salt 5 parts Methanol 360 parts Water 50 parts In this recipe, the binder and photosensitive Diazo compound are dissolved in the mixture of methanol and water. The solution is coated over the layer 11 of the paper to about 3 mils thickness and permitted to dry. The dried coating is somewhat yellowish in color and has the soft surfaced opaque appearance typical of blushed lacquer coatings. More detail on this example,

and other alternatives may be obtained from US. Pat.

No. 3,377,165 to Workman.

From the foregoing, it will be understood that a variety of materials and techniques may be utilized to produce the heat sensitive two-color printing embodiment of FIG. 1. While red and black are usually believed most desirable for two-color applications, changing dyes and utilizing variations in the component selection for the heat sensitive reaction system makes it possible to obtain a wide variety of colors.

Referring now to FIG. 2, an alternate form of paper in accordance with the present invention is illustrated.

The process of forming the paper of FIG. 2 involves first coating the base paper 10 with a layer 15 of black ink or dye. This is followed by a second coating 16, which is a high temperature blush coating, preferably dyed red. On top of this is applied a lower temperature opaque, near white blush coating 17. When a low quantity of heat is applied to the top white blush coating 17, it becomes transparent to expose the red of lower blush coating 16. With a high thermal input, both blush coatings l7 and 16 become transparent, exposing the black coating 15, which gives an ultimate black or near black image to the eye of the viewer. As illustration of this embodiment follows.

EXAMPLE 6 In accordance with the example, the white base stock or paper 10 is coated with a standard oil-soluble black dye. Any oil-soluble black dye may be utilized and the proportions are unimportant so long as a distinct and intense black color is imparted to directly overlie the surface 10 of FIG. 2. Alternatively, a black dye is made by utilizing Iampblack, cellulose acetate and 85% acetone. The resulting black layer is allowed to dry.

The red blush coating layer 16 is prepared from an oxidized polyethylene wax, with molecular weight from 3,000 to 5,000, a melting point ranging between 100 and 150 C., such as the commercially available wax known as Hoechst PAD 532. The wax is dispersed in a water-binder solution to which has been added a small proportion of red water-soluble dye, for example normal food coloring dye obtainable commercially under the label French. The relative proportions (by weight) are as follows: 30 parts of wax mixed with 170 parts of a water solution consisting of 4 weight percent methylcellulose, A weight percent red dye, and 95% weight percent water. These combined materials are ball milled until the wax is divided into small particles, on the order of about 1 micron size, to suspend in the methylcellulose-dye solution. If difficulty is experienced with foaming, an anti-foam agent may be added if desired (see the discussion in connection with Example 1 herein, relating to preparation for the materials for layer 12).

The high melting wax suspension obtained after ball milling is completed is coated to overlie black layer 15, and forms the red blush coating layer 16. It is desirably applied to a dried thickness of a few microns, e.g., about IO microns, and the standard application techniques, discussed previously herein, are utilized.

Materials for the blush coating 17 are provided by utilizing wax having a lower melting point than that selected for the materials of preparation of the layer 16, described above. In this example, the melting point of the wax selected is between 50 and 100 C. and the specific wax utilized in this example is micro crystalline paraffin wax. Ten parts by weight of wax are dispersed in the following solution (on a parts by weight basis): 10 parts cellulose acetate; 15 parts water; 75 parts acetone.

The dispersing of the wax is again accomplished by ball milling until micron-sized particles are obtained which suspend in the solvent system.

Thereafter, the materials for the low melting blush layer 17 (i.e., the wax melting in the range of 50I00C., e.g.) are applied, as by Mayer bar, to obtain a layer of a few microns thickness, on the order of about 10 microns (when dry). On drying, the white blush coating on layer 17 results and the end product illustrated in FIG. 2 is completed and ready for utilization.

In use, the application of heat in preselected areas causes opaque layer 17 to transparentize in the regions of heat application to allow the color of layer 16 to be exposed. On low heat application, the layer 16 will not transparentize and will therefore present a red color to the viewer looking at the upper surface of the product of FIG. 2. On the other hand, in those regions where higher heat application is selectively applied, not only will the top layer 17 transparentize but so will the underlying layer 16 transparentize. In this condition, the

8 viewer sees the underlying layer 15, and his eye perceives a predominantly black coloring, as a result of the substantial visibility of the black coating or layer 15 through the transparentized layers above.

In connection with the embodiment of FIG. 2, it will be readily understood that a variety of colors and dyes may be utilized, as desired, to obtain the end result of providing heat sensitive two-color printing.

Having described the invention in connection with certain specific embodiments thereof, it will be understood that further modifications may now suggest themselves to those skilled in the art and it is intended to cover such modifications as fall within the scope of the appended claims.

What is claimed is:

1. A heat sensitive, sheet material, comprising:

a. a supporting substrate;

b. a first layer of a first color of heat actuable material, responsive to a first quantity of heat to change to a second color; and

c. a second layer of a normally substantially opaque coat overlaying the first layer, responsive to a second quantity of heat less than the first quantity of.

heat to be transparentized.

2. The heat sensitive sheet material of claim 1 wherein the first layer comprises a material having a dye dispersed therein to provide the first color, the material being responsive to the application of the first quantity of heat to change to a color which combines with the dye to provide the second color.

3. The heat sensitive sheet material of claim 1 wherein the supporting substrate is a paper base layer.

4. A heat sensitive sheet material comprising:

a. a supporting substrate;

b. a first layer of a material of a first color overlaying the substrate;

0. a second layer of a normally substantially opaque coat overlaying the first layer, responsive to a first quantity of heat to be transparentized; and

d. a third layer of a normally substantially opaque coat overlaying the second layer, responsive to a second quantity of heat less than the first quantity of heat to be transparentized.

5. The heat sensitive sheet material of claim 4 wherein the supporting substrate is a paper base layer.

6. A method of forming a heat sensitive sheet material comprising the steps of:

a. preparing a color formulation of a first color that is changeable to a second color upon application of heat;

b. applying the formulation to a supporting substrate;

and

c. applying a substantially opaque blush coat solution over the formulation, the solution becoming transparent upon application of heat.

7. The method of claim 6 having the additional step of drying the formulation after applying it to the substrate.

8. The method of claim 7 wherein the substrate is a paper base layer.

9. The method of forming a heat sensitive sheet material comprising the steps of:

a. preparing a formulation of a first color b. applying the formulation to a supporting substrate;

c. applying a first substantially opaque blush solution to the formulation, the solution becoming transparent upon application of a first amount of heat; and

d. applying a second substantially opaque blush solu- 10. The method of Claim 9 wherein the supporting tion over the first solution, the second solution becoming transparent upon application of a second amount of heat, less than the first amount.

substrate is a paper base sheet. 

1. A HEAT SENSITIVE, SHEET MATERIAL, COMPRISING: A. A SUPPORTING SUBSTRATE; B. A FIRST LAYER OF A FIRST COLOR OF HEAT ACTUABLE MATERIAL, RESPONSIVE TO A FIRST QUANTITY OF HEAT TO CHANGE TO A SECOND COLOR; AND C. A SECOND LAYER OF A NORMALLY SUBSTANTIALLY OPAQUE COAT OVERLAYING THE FIRST LAYER, RESPONSIVE TO A SECOND QUANTITY OF HEAT LESS THAN THE FIRST QUANTITY OF HEAT TO BE TRANSPARENTIZED.
 2. The heat sensitive sheet material of claim 1 wherein the first layer comprises a material having a dye dispersed therein to provide the first color, the material being responsive to the application of the first quantity of heat to change to a color which combines with the dye to provide the second color.
 3. The heat sensitive sheet material of claim 1 wherein the supporting substrate is a paper base layer.
 4. A heat sensitive sheet material comprising: a. a supporting substrate; b. a first layer of a material of a first color overlaying the substrate; c. a second layer of a normally substantially opaque coat overlaying the first layer, responsive to a first quantity of heat to be transparentized; and d. a third layer of a normally substantially opaque coat overlaying the second layer, responsive to a second quantity of heat less than the first quantity of heat to be transparentized.
 5. The heat sensitive sheet material of claim 4 wherein the supporting substrate is a paper base layer.
 6. A method of forming a heat sensitive sheet material comprising the steps of: a. preparing a color formulation of a first color that is changeable to a second color upon application of heat; b. applying the formulation to a supporting substrate; and c. applying a substantially opaque blush coat solution over the formulation, the solution becoming transparent upon application of heat.
 7. The method of claim 6 having the additional step of drying the formulation after applying it to the substrate.
 8. The method of claim 7 wherein the substrate is a paper base layer.
 9. The method of forming a heat sensitive sheet material comprising the steps of: a. preparing a formulation of a first color b. applying the formulation to a supporting substrate; c. applying a first substantially opaque blush solution to the formulation, the solution becoming transparent upon application of a first amount of heat; and d. applying a second substantially opaque blush solution over the first solution, the second solution becoming transparent upon application of a second amount of heat, less than the first amount.
 10. The method of claim 9 wherein the supporting substrate is a paper base sheet. 